Method for preparation of disodium pamidronate

ABSTRACT

The invention includes a method for the preparation of disodium pamidronate comprising: (a) preparing a stirred slurry of pamidronate in water, (b) adding a solution of sodium hydroxide to give a clear solution at pH of about 6.5, (c) filtering the solution and (d) freezing and lyophilizing the solution to give an amorphous essentially anhydrous disodium pamidronate which contains ≦2 wt-% water.

BACKGROUND OF THE INVENTION

Disodium 3-amino-1-hydroxypropane-1,1-diphosphonate or "disodium pamidronate" has the formula: ##STR1##

It is commercially available as the lyophilized pentahydrate, under the name AREDIA® from Novartis Pharmaceuticals Corp., and is used to inhibit bone resorption, i.e., to treat moderate or severe hypercalcemia associated with malignancy, with or without bone metastases. The preparation of the crystalline pentahydrate from pamidronic acid is disclosed by Stahl et al. in U.S. Pat. Nos. 4,711,880 and 4,639,338. This material is prepared by partially neutralizing a heated slurry of pamidronic acid with aqueous sodium hydroxide (NaOH) to pH 7-7.5 and then initiating crystallization at ≧50° C. The mixture is slowly cooled to 0-5° C. and the disodium pamidronate is collected by filtration. This product is described as having "excellent crystallinity" and as being "completely stable to storage under approximately normal ambient conditions." It comprises about 24.1-25% water.

The crystalline product ("Modification E") is contrasted with an amorphous product disclosed to be prepared by the general process of Jary et al. (U.S. Pat. No. 4,304,734). In Comparison Example 1 of the '338 patent, pamidronic acid is neutralized to pH 7.4 with aqueous NaOH and the reaction mixture is concentrated to dryness under reduced pressure at 60-70° C. and then dried at 20 mbar to constant weight. However, the amorphous product that is obtained is described as deliquescent in air, contains 12.9% of retained water and, as taught in the '338 patent, will convert to the pentahydrate. Stahl et al. also teach the interconversion of other crystalline forms of disodium pamidronate depending upon humidity and amount of water present, which demonstrates the difficulty in utilizing preformed disodium salts of pamidronic acid for further processing into sterile pharmaceutical dosage forms.

Thus, a need exists for a simple method to prepare disodium pamidronate that is stable to storage and suitable for reconstitution and intravenous infusion/injection.

SUMMARY OF THE INVENTION

The present invention provides a method for the preparation of amorphous, essentially anhydrous (≦1-2 wt-% water) disodium pamidronate (the "product"). The product of the invention can be stored under nitrogen at otherwise ambient conditions, and readily reconstituted with sterile water or physiological salt solutions for injection or infusion into a patient in need of treatment therewith.

The method comprises addition of aqueous sodium hydroxide to a stirred slurry of pamidronic acid in an about 2:1 molar ratio of NaOH to acid, optionally comprising excess mannitol, to yield a clear solution of pH 6.5±0.1. Aqueous phosphoric acid is added as needed if the pH following NaOH addition is too high. A small amount of aqueous NaOH can be added if the pH is too low. Preferably, 1 N aqueous NaOH is used.

The solution is frozen and lyophilized under reduced pressure to yield amorphous, essentially anhydrous disodium pamidronate. The product is stable when stored under dry nitrogen at otherwise ambient conditions.

Preferably, the about pH 6.5 solution is filtered and aliquots are introduced into suitable container(s), then frozen (-25 to -40° C.), lyophilized (10-25 mbar, 20-40° C.) in situ, and the containers sealed under positive nitrogen pressure to yield a plurality of unit dosage forms of disodium pamidronate, optionally in admixture with mannitol.

For example, vials containing 30 mg, 60 mg and 90 mg of sterile lyophilized disodium pamidronate, each optionally containing 470 mg, 400 mg, and 375 mg of mannitol can readily be prepared and utilized as disclosed in Physician's Desk Reference (52d ed., 1998) at pages 1824-1828.

As used herein, the term "about" incorporates inherent variability of the parameter referenced, due to measurement techniques known to the art, i.e., pH, or water content (loss on drying).

DETAILED DESCRIPTION OF THE INVENTION

The invention will be further described by reference to the following detailed example.

EXAMPLE 1 Preparation of Disodium Pamidronate

For a batch size of 5 L, 587.5 g (3.2 moles) of mannitol is dissolved in 3.5 L of water. Pamidronic acid (31.6 g, 0.133 moles) is mixed with a 1.0 L aliquot of the mannitol solution to form a slurry. The slurry is then transferred into the remainder of the mannitol solution, and stirred for at least 15 min. Aqueous 1 N sodium hydroxide (270 ml) is then added and the mixture is stirred until a clear, colorless solution results. The pH is then adjusted to 6.5±0.1 using either 1 M aqueous phosphoric acid or 1 N aqueous sodium hydroxide, as needed. The solution is then filtered through a 0.22 micron filter, and filled at 20° C. into vials at 4.0 ml (4.172 g)/vial, under sterile conditions. The aqueous solution is frozen at -37° C. and lyophilized (20 mbar, 20-40° C.) to yield 1,250 vials, each containing 30 mg of amorphous disodium pamidronate. The vials are sealed under positive nitrogen pressure. The disodium pamidronate is amorphous (noncrystalline) by X-ray diffraction and contains 0.7 wt-% water (USP 23 <731>).

Alternatively, the present product can be formulated for oral administration as disclosed, for example, in Bechard (U.S. Pat. No. 5,431,920) or Strein (U.S. Pat. No. 5,366,965).

All publications, patents and patent documents are incorporated by reference herein, as through individually incorporated by reference. The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention. 

What is claimed is:
 1. A method for preparing disodium pamidronate comprising:(a) preparing a stirred slurry of pamidronic acid in water; (b) adding aqueous solution of sodium hydroxide to said slurry in an about 2:1 molar ratio of sodium hydroxide to pamidronic acid; to yield a clear solution having a pH of about 6.5; (c) filtering said solution; and (d) freezing and lyophilizing said filtered solution to yield amorphous, essentially anhydrous disodium pamidronate.
 2. The method of claim 1 wherein said slurry comprises mannitol.
 3. The method of claim 1 or 2 wherein, in step (d) a plurality of aliquots of solution are filled into a plurality of storage vessels, frozen and lyophilized in situ.
 4. The method of claim 3 wherein the amorphous, essentially anhydrous disodium pamidronate is sealed into said vessels under positive dry nitrogen pressure.
 5. The method of claim 1 wherein the essentially anhydrous disodium pamidronate contains ≦2 wt-% water.
 6. The method of claim 1 wherein the solution is frozen at about -25° C. to -40° C.
 7. The method of claim 1 wherein the lyophilization is carried out at about 20-40° C. at about 10-25 mbar. 